Compounds of the above formula where R.sub.1 is alkyl(C.sub.1 -C.sub.3) and R.sub.2 is hydrogen are disclosed generically in U.S. Pat. No. 4,115,572 as anti-asthmatic agents. Specifically these compounds are 4-ethyl-8-methylimidazo[1,5-d]-1,2,4-triazin-1(2H)-one and 8-methyl-4-propylimidazo[1,5-d]-1,2,4-triazin-1,(2H)-one.
Compounds of the above formula where R.sub.1 is hydrogen and R.sub.2 is other then hydrogen are considered new compounds which are not disclosed in any U.S. patent. Specifically these compounds are:
8-methyl-6-(3-pyridinyl)imidazo[1,5-d]-1,2,4-triazin-1-(2H)-one PA0 8-methyl-6-(1-naphthalenyl)imidazo[1,5-d]-1,2,4-triazin-1-(2H)-one PA0 8-methyl-6-(2-pyridinyl)imidazo[1,5-d]-1,2,4-triazin-1-(2H)-one PA0 8-methyl-6-(4-methylphenyl)imidazo[1,5-d]-1,2,4-triazin-1-(2H)-one
These compounds may be prepared by the procedure shown in the following flowchart.